Seasonal hair shedding

Late September. The days are getting shorter, and there’s more hair than usual in the shower. You vaguely remember it was the same last year, around this time. You’re not imagining it: the French Society of Dermatology (SFD) describes shedding that is often heavier in spring and especially in autumn¹.

This rhythm isn’t just a feeling. It has been measured, in men and in women, and it comes down to the hair growth cycle.

Why autumn

Each hair goes through a long growth phase, then a resting phase (the telogen phase). While resting, it no longer grows. It stays in place for two to four months, then the new hair growing underneath pushes it out³.

It all starts in summer. That’s the season with the largest share of resting hairs². Add the few months’ delay before they fall, and you land in late summer and autumn. The shedding you see in October was set up in July.

What the studies measured

The clearest measurement comes from England. In Sheffield, researchers followed 14 men aged 18 to 39 for 18 months, with a check every 28 days. The share of growing hairs peaked at over 90% in March, then fell steadily until September. Hairs shed peaked around August and September: about 60 a day, more than twice the level of the winter before⁴.

That’s very few people, men only, all working indoors in the same city. But two other studies point the same way.

In Zurich, a team went back through six years of records of women who had come in about hair loss. After ruling out those with an illness or medicine known to cause shedding, 823 were left. Microscope checks of their hair show a yearly rhythm: the largest share of resting hairs in summer, and the smallest at the end of winter². These women were worried about their hair, so they don’t represent the whole population. Still, the authors note it’s the first systematic study on this many women².

In France, researchers from the L’Oréal laboratory photographed the same small patch on top of the scalp of 10 men for 8 to 14 years. The result: the most resting hairs at the end of summer and the start of autumn, and a rhythm linked to sunlight⁵. Again, very few participants, and a study run by a cosmetics company.

Despite very different methods and participants, all three studies find the same calendar. All three were done in the northern hemisphere: they say nothing about what happens south of the equator.

What about spring?

The SFD names spring as a second shedding period¹. The Zurich study also sees a second peak in spring, smaller than the summer one². In the French study, some men had two peaks a year, others only one⁵. Not everyone has the same rhythm, and in men with very few resting hairs, the researchers found no rhythm at all⁵.

So if you don’t notice anything special in autumn, that’s normal too.

How long it lasts

The studies don’t give an exact duration. They give landmarks. The shedding peak falls around August and September⁴, and the share of resting hairs is lowest at the end of winter². In practice, seasonal shedding spreads over late summer and autumn, then calms down over the winter.

For comparison, shedding set off by a shock (a high fever, giving birth, a crash diet) usually lasts 3 to 6 months. Beyond 6 months, dermatologists call it chronic shedding³. Seasonal shedding that runs well into spring is no longer just seasonal shedding.

What helps, what doesn’t

There’s nothing to cure. The hairs that fall in autumn are replaced by hairs already growing underneath³.

Be wary of “autumn special” supplement courses. The authors of the French study stress that the season has to be taken into account when judging an anti-hair loss treatment⁵. A product started in October can seem to work by January, just because shedding season is over.

Looking after your hair stays simple: no vigorous brushing, less straightening and fewer blasts of very hot air, no tight hairstyles, enough iron and protein in your diet³. These habits don’t stop the cycle, they just avoid adding breakage on top. As for supplements, DermNet recommends correcting a lack of iron, vitamin B12 or folate when a blood test shows one⁶.

When it’s not just the season

The third point matters most. Shedding can reveal pattern hair loss that was already on its way⁶, meaning a gradual thinning of the hair in certain areas. So seasonal shedding that doesn’t end can be hiding something else. A dermatologist can tell you whether you have temporary shedding, hair loss or both⁷. If it’s pattern hair loss, your doctor can offer you a treatment, and the earlier it starts, the better the results⁷.

Compare a season with the same season

The trap with seasonal shedding is the comparison. If you compare your hair in October with your hair in April, you’re comparing the low point and the high point of the cycle. You may think things are getting worse when all you’re seeing is the season.

The most reliable way is to take the same photo every week: same room, same light, same distance, hair dry and styled the same way. Aim at your part, the crown and your forehead. After a year, you can put this October’s photo next to last October’s: two points in the same rhythm.

That’s what Calvap lets you do. Your last photo appears as a see-through overlay so you can line up in the same spot, and your photos stay on your phone, sorted by area and date. You see whether the volume comes back after autumn, or keeps dropping from one year to the next. If it does, you have dated photos to show your doctor.